1. Field of the Invention
The present invention relates to a roller and cage assembly.
2. Description of the Prior Art
Roller and cage assemblies that took advantage of characteristics such as having a small cross-sectional height, large load capacity and favorable high-speed rotation performance were frequently used in the past for the connecting rods of engines installed on motorcycles and so forth.
FIGS. 1 through 4 show an example of a roller and cage assembly of the prior art. Furthermore, this roller and cage assembly is disclosed in Japanese Utility Model Laid-Open Publication No. 52-124353.
As shown in the drawings, this roller and cage assembly is composed of a roughly cylindrically shaped cage 1, in which a plurality of pockets la are formed at equal intervals in the circumferential direction, and rollers 2 (not shown in FIG. 2), which have a larger diameter than the wall thickness of said cage 1 and are inserted into each of said pockets 1a. Cage 1 has two rings 1b, one on either end, and a plurality of thin-walled columns 1c (or bars 1c in the nomenclature of International Standard Organization ISO5593), which are integrated into a single structure with both said rings 1b and are arranged in the circumferential direction to as to demarcate the above-mentioned pockets 1a together with said rings 1b. The end surfaces of both sides in the circumferential direction of each of said columns 1c serve as roller guide surfaces 1d. In addition, inner retaining projections 1e and outer retaining projections if are respectively formed on both sides in the circumferential direction at the center and both ends of each of said columns 1c. These inner retaining projections 1e and outer retaining projections if prevent roller 2 from falling out to the inside and outside.
As is clear from FIGS. 1 through 3, the central portion of each of the above-mentioned columns 1c is bent to the inside so that it forms the letter "M" together with the cross-sectional shape of rings 1b of both ends. This roller and cage assembly is therefore referred to as an M-shaped roller and cage assembly.
In the roller and cage assembly having this constitution, since columns 1c are thin-walled and bent considerably, the rigidity of cage 1 is limited. This cage is frequently selected in the case of being subjected to relatively weak loads. On the other hand, with respect to lubrication, since this roller and cage assembly is able to adequately take in lubricant by taking advantage of its largely opened M-shaped cross-section, lubrication is performed extremely efficiently. Consequently, even if the amount of lubricant supplied is low, the roller and cage assembly is able to continue to rotate at high speeds for a long time.
FIGS. 5 through 7 indicate another example of a roller and cage assembly of the prior art. Furthermore, this roller and cage assembly is disclosed in Japanese Patent Laid-Open Publication No. 1-299317. In addition, since this roller and cage assembly is composed in the same manner as the roller and cage assembly shown in FIGS. 1 through 4 with the exception of those portions explained below, an explanation of the entire roller and cage assembly is omitted. Instead, only the essential portion will be explained. In addition, in the following explanation, the same reference numerals will be used for those constituents identical or corresponding to the constituents of the roller and cage assembly shown in FIGS. 1 through 4.
In this roller and cage assembly, each of columns 1g,which demarcate pockets la together with rings 1b on both ends, is composed in the following manner.
Namely, column 1g has guide portions 1h, respectively continuous with both rings 1b and formed to be thick-walled from the outside to the inside of the pitch circle diameter (P.C.D.) of roller 2, and thin-walled portion 1i interpositioned between said guide portions 1h, and are formed so that the outer surface is roughly consistent with the outer peripheral surface of ring 1b over its entire length. Roller guide surface 1j (see FIG. 7) is formed on both sides in the circumferential direction of both said guide portions 1h. In addition, inner retaining projections 1k are formed on both sides in the circumferential direction of the inner surface of said both guide portions 1h, and outer retaining projections 1m are formed on both sides in the circumferential direction of thin-walled portion 1i. Roller 2 is retained by these projections, and is prevented from falling out of pocket 1a.
As is clear from FIGS. 5 and 6, each of the above-mentioned columns 1g is formed into the shape of a gateway together with the cross-sectional shape of both rings 1b. As a result, this roller and cage assembly is referred to as a gateway-shaped roller and cage assembly.
Since this roller and cage assembly has a cross-section in the shape of a gateway as described above, it has large rigidity. In addition, since the width dimension of columns 1g along the P.C.D. of roller 2 is smaller than the M-shaped roller and cage assembly previously described, the number of rollers 2 incorporated can be increased. As a result of having these characteristics, this roller and cage assembly is selected when a high load capacity is required. However, this roller and cage assembly has the following problems with respect to lubrication.
Namely, as shown in FIG. 8, the state in which this roller and cage assembly is equipped on the big end 6a of a connecting rod 6 is considered. At this time, the supply of lubricant (oil) to said roller and cage assembly is performed through weights 7a of crankshaft 7, side slits 8 between cage 1, and center slit 6b formed in the center in the axial direction of big end 6a. Center slit 6b, however, is expected to supply the largest amount of lubricant. However, in said roller and cage assembly, guide portions 1h (see FIG. 6), in which roller guide surfaces 1j (see FIG. 7) are formed, are located on both end surfaces of cage 1, and are greatly removed from center slit 6b. Thus, a large amount of lubricant must be supplied to prevent seizure during high-speed rotation.
In addition, in said roller and cage assembly, the end surfaces of cage 1 and corresponding end surfaces of big end 6a generate wear as indicated with the double dot broken line as shown in FIG. 9 following high-speed rotation testing. Since thick-walled guide portions 1h are provided on said end surfaces as described above, mass ends up becoming imbalanced. Thus, the above-mentioned wear is the result of this end surface portion, in which the distribution of mass is large, making strong contact with big end 6a. Namely, since the pV value becomes locally high, in order to obtain favorable high-speed rotation performance, the amount of lubricant supplied must be increased with respect to this point as well.